PAPERS ON CHEMISTRY AND PHYSICS 291 



A considerable number of soils which are high in or- 

 ganic carbon content were found to give high lime-re- 

 quirements by the Veitch and Jones methods. On chart- 

 ing all the results in order of increasing content of or- 

 ganic carbon, however, no indication was observable of 

 a causal relationship. When all the results were similar- 

 ly charted in order of increasing total calcium content of 

 soil, no relationship whatever was found between total 

 calcium and lime-requirement as determined by any 

 method. 



The wide divergence between the Hopkins method on 



the one hand, and the Veitch and Jones methods on the 



* 

 other, is in accordance with what one might expect when 



the principles involved in the methods are considered. 

 The Veitch method measures essentially the total absorb- 

 ing power of the soil for the free base, since Ca (OH) 2 is 

 the reagent used. The absorbing capacity of the soil is 

 a lesser factor in the Jones calcium acetate method, the 

 calcium ions being in equilibrium with those of a weak 

 acid, while in the Hopkins method absorption phenomena 

 are more largely excluded. Potassium ions, which under 

 similar conditions are absorbed more readily by most 

 soils than are calcium ions, are here combined with a 

 strong acid into one of the most stable salts. It is alto- 

 gether probable' that absorption plays some part in the 

 exchange of bases which occurs in this determination, 

 as a result of which aluminum salts are brought into solu- 

 tion. These undergo hydrolysis, yielding an acid solu- 

 tion which may be titrated until all the aluminum is pre- 

 cipitated as the hydroxide. It is of interest to note that 

 Dr. Veitch criticized the Hopkins method when it first 

 appeared on the ground that it was essentially a method 

 for the determination of soluble aluminum in soils. At 

 that time aluminum was not recognized as a factor in the 

 toxicity of acid soils to crops. The discovery of alumi- 

 num toxicity has converted this objection into an advan- 

 tage for the method. 



It may be observed that the divergence between the 

 Hopkins, and the Veitch and Jones methods is slightly 

 greater in the soils represented in Figs. 3, 4, and 5, than 

 in those of Figs. 1 and 2. The former three groups con- 



